Method in the preparation of progressive-burning smokeless powder



Patented Mar. 28, 1939 STATES METHOD IN THE PREPARATION OF PRO- GRESSIVE-BURNING SMOKELESS POW- DER Bernhart Troxler, Kenvil, N. J., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September 9, 1937, Serial No. 163,155

7 Claims.

This invention relates to an improved method in the preparation of progressive-burning smokeless powder and more particularly to an improved method of coating smokeless powder with a deterrent material.

As is well known, in order to render possible close control of the burning rate of smokeless powder and produce a high velocity of the projectile without high breech pressures, it has been customary to coat the grains of the smokeless powder with a deterrent material, explosive or non-explosive, which will retard the initial burning rate of the powder grains. Such coating material penetrates the powder grains more or less, so that as the powder burns, the succesively exposed surfaces contain gradually less and less of the deterrent material, thus causing the combustion of the grains to proceed with increasing speed.

In order to effect the coating of smokeless powder grains with a deterrent material, numerous processes have been devised, e. g., using dinitrotoluene, mononitronaphthalene, or diethyldiphenyl urea; the powder grains are coated by treatment with a solution of these coating materials in a volatile vehicle which is a non-solvent or a weak solvent for the powder grains and agitated with the said powder grains at the desired temperature. The volatile vehicle is then evaporated and penetration into the grain of powder obtained by immersing the coated powder grains in a hot bath for several hours or days. However, when it is necessary to apply high percentages of the deterrent material to the powder grain it is difficult to prevent the individual powder grains from adhering to each other or forming clusters, which thus reduces the yield of usable powder.

By another method the powder grains are wet with water while tumbling in a sweetie barrel, to which the undissolved coating agent is added, and the mixture then heated to the melting point of the coating agent. The molten coating material forms an oily film on the water surrounding each grain of powder, and as it comes in contact with the powder, due either to the evaporation of the water or the adsorption of the water by the powder grain, deposits on the surface of the powder grain. This method is quite satisfactory when only a very thin coating layer is necessary to properly deter the powder, but when relatively heavy coating layers are required, the solvent action on the surface of the powder grains is such as to cause the grains to adhere to each other and form clusters similarly to the prior process above mentioned and hence open to the same objections.

Now in accordance with my invention I have found that I may appreciably reduce the number of clustered grains when applying a heavy coating and thus obviate this disadvantage of the prior processes. Specifically I have found that by add ing the deterrent material in more than one increment,.in the presence of water, and allowing time for each increment to penetrate to a considerable degree into the powder, that the concentration of the coating material on the surface at any one time is reduced, and so the amount of clustered powder is reduced. The number of increments, and the size of each, will depend upon the nature of the coating material, the amount necessary for deterrence and the surface area of the powder. I may, for example, add the total deterrent to be applied in two increments allowing from about 45 minutes to about 1 hour between successive additions, or I may add the total deterrent to be applied in more than two increments allowing only about 15 minutes between successive additions, or I may use various other combinations depending upon the factors above mentioned.

My improved method is particularly applicable when solvent plasticizers are used, which penetrate into the powder grain slowly because of their high viscosity, the complexity of the molecule, or for other reasons not clearly understood. Specifically I have found that my improved method of coating is particularly advantageous when'using materials which melt between 45 C. and 95 C., and which, molten, will cause swelling of a thin section cut from a powder grain, which continues until the original grain structure is. no

longer apparent, although individual fibers may be undispersed.

As examples of substances suitable for use as coating agents according to my improved process, I may mention dinitrotoluene, symmetrical diethyldiphenyl urea, triphenyl phosphate, mononitronaphthalene, phenyl benzoate, ethyl-o-benzoyl benzoate, etc.

The procedure in accordance with this invention is more specifically illustrated by the following examples.

Example I 906 parts by weight of a 15% nitroglycerine powder pressed through a 0.038 inch die, granulated 1'75 cuts per inch were coated with a total of 30 parts by weight of symmetrical diethyldiphenyl urea in increments as follows: The powder was heated at about C. and parts by weight of water added. After the water was thoroughly admixed with the powder, 9 parts by weight of powdered symmetrical diethyldiphenyl urea were sprinkled in, the powder and symmetrical dieth/ldiphenyl urea tumbled together at a tempf/f'ature of 70 C., for 15 minutes, after which 40 parts by weight of water and 4 parts by weight of symmetrical diethyldiphenyl urea were added and this procedure repeated every 15 minutes until a total of 30 parts by weight of symmetrical diethyldiphenyl urea were added. In the last increment only 3 parts by weight of symmetrical diethyldiphenyl urea were added. Heating was continued until the total time of heating in the coating barrel was 1 hours. After drying and screening the powder, it was found that 76% of the powder remained unclustered and was satisiactory for use.

In comparison with this, I coated 906 parts by weight of this same type of powder, wet with90 parts by weight of water, with 30 parts by weight of symmetrical diethyldiphenyl urea sprinkled inas one portion in the sweetie barrel which was then run at 70 C. for one hour. After drying and screening, I found that only 63% of the powder was satisfactory, but this contained a number of pellets of two and three grains stuck together which were not removed in the screening operation. I

Ewample II V 906 parts by weight of a 20% nitroglycerine powder pressed through a 0.064 inch die having a 0.020 inch pin, and cut 11 cuts per inch, were coated with a total of 36.2 parts by weight of triphenyl phosphate in increments as follows in a sweetie barrel. The powder was wet with 91 parts by weight of water and 9.2 parts by weight of triphenyl phosphate sprinkled in. After tumbling in the sweetie barrel for 15 minutes at a temperature of C., 45 parts by weight of water and 9 parts by weight of triphenyl phosphate were added. After another 15 minute interval of tumbling, an additional 9 parts by weight of triphenyl phosphate were added without additional water. The remaining 9 parts by weight of triphenyl phosphate were added without water after an additional 15 minutes of coating. The total time of coating was 1 hour. The powder was then dried for 3 days at 55 C., glazed with graphite and screened. There was 83% of unclustered powder.

In comparison with this, 906 parts by weight of this same powder were wet with 91 parts by Weight of water and coated with 36.2 parts by weight of triphenyl phosphate, all of which was added at the beginning of the coating operation. This powder was coated for one hour at 75 C. and finished in the same manner as that above.

By this procedure only 10% of unclustered powder was obtained in comparison with 83% according to my improved method.

Example III 906 parts by weight of a 20% nitroglycerine powder pressed through a 0.064 inch die having a 0.015 inch pin and cut 11 cuts per inch, were coated with a total of 90.6 parts by weight of dinitrotoluene in a coating barrel added in increments as follows. The powder grains were wet with 27 parts by weight of Water and one half of the total dinitrotoluene added. After 15 minutes, an additional 18 parts by weight of water were added together with one half of the remaining dinitrotoluene. The' powder was tumbled for 15 minutes more, after which 18 parts by weight of water were again added together with the remainder of the dinitrotoluene. The total coatingtime was one hour and the coating temperature was maintained at C. After finishing the powder as in the previous example 94.8% of unclustered powder resulted;

In comparison with this,;906 parts by weight of this same powder were wet with 27 parts by Weight of water and a total of 90.6 parts by weight of dinitrotoluene added at the beginning of the coating operation. The powder was coated for one hour at 85 C. and finished as in the above examples. I found only 16% of unclustered powder in comparison with practically 95%, when using my improved process.

It will be understood that the examples given are for illustrative purposes only and that various modifications may be made in the method of applying the deterrent without departing from the scope of this invention.

What I claim and desire to protect by Letters Patent is:

1. A process for the preparation of unclustered progressive-burning smokeless powder which includes coating smokeless powder in the presence of water with successive substantial fractions of the total deterrent to be applied, the said deterrent when molten being a solvent for nitrocellulose and being applied in the molten state and characterized by a melting point within the range of about 45 C. to about 95 C.

2. A process for the preparation of unclustered progressive-burning smokeless powder which includes coating smokeless powder grains in the presence of water with dinitrotoluene in the molten state, said dinitrotoluene being added in successive substantial fractions of the total to be applied.

3. A process for the preparation of unclustered progressive-burning smokeless powder which includes coating smokeless powder grains in the presence of water with triphenyl phosphate in the molten state, said triphenyl phosphate being added in successive substantial fractions of the total to be applied.

4. A process for the preparation of unclustered progressive-burning smokeless powder which includes coating smokeless powder grains in the presence of water with symmetrical diethyldiphenyl urea in the molten state, said symmetrical diethyldiphenyl urea being added in successive substantial fractions of the total to be applied.

5. A process for the preparation of unclustered progressive-burning smokeless powder which includes coating smokeless powder grains in the presence of water with symmetrical diethyldiphenyl urea in the molten state in successive fractions of the total deterrent to be applied, the first fraction consisting of about 30% of the total followed after approximately 15 minute intervals by about 15% increments of the total, the last increment consisting of about 10% of the total.

6. A process for the preparation of unclustered progressive-burning smokeless powder which includes coating smokeless powder grains in the presence of water with triphenyl phosphate in the molten state in successive fractions of the total deterrent to be applied, said triphenyl phosphate being added at approximately 15 minute intervals, in increments of about 25% of the total 

